Grown and artificial mosaic GaAs crystals for hard X-ray astronomy

In order to increase the collection efficiency of a lens for hard X-ray energies, mosaic GaAs crystals to be used as optic elements in Laue diffraction are proposed. In fact, GaAs crystals show a natural degree of mosaicity due to the spontaneous formation during the growth of cellular structures with dislocations at the boundaries. Several GaAs samples grown by LEC method have been characterized by means of high-resolution X-ray diffraction. Mosaicity values ranging from 10 to 25 arcsec have been measured. Since proper growth conditions allow to control and modify both the dislocation density and the cellular structure responsible of the mosaic spread, the possibility of obtaining crystals with a given degree of mosaicity by tuning the LEC growth conditions is proposed. A complementary strategy to increase the Darwin width of the diffraction curve based on curved crystals has also been proposed. The lattice curvature was achieved by introducing a compressive stress on the crystal surface. Curvature radii between 2 and 8m were easily obtained in wafer crystals 500 μm thick

Catchment features controlling nitrogen dynamics in running waters above the tree line (central Italian Alps)

The study of nitrogen cycling in mountain areas has a long tradition, as it was applied to better understand and describe ecosystem functioning, as well as to quantify long-distance effects of human activities on remote environments. Nonetheless, very few studies, especially in Europe, have considered catchment features controlling nitrogen dynamics above the tree line with focus on running waters. In this study, relationships between some water chemistry descriptors – including nitrogen species and dissolved organic carbon (DOC) – and catchment characteristics were evaluated for a range of sites located above the tree line (1950–2650 m a.s.l.) at Val Masino, in the central Italian Alps. Land cover categories as well as elevation and slope were assessed at each site. Water samples were collected during the 2007 and 2008 snow free periods, with a nearly monthly frequency. In contrast to dissolved organic nitrogen, nitrate concentrations in running waters showed a spatial pattern strictly connected to the fractional extension of tundra and talus in each basin. Exponential models significantly described the relationships between maximum NO3 and the fraction of vegetated soil cover (negative relation) and talus (positive relation), explaining almost 90% of nitrate variation in running waters. Similarly to nitrate but with an opposite behavior, DOC was positively correlated with vegetated soil cover and negatively correlated with talus. Therefore, land cover can be considered one of the most important factors affecting water quality in high-elevation catchments with contrasting effects on N and C pools

Focusing effect of bent GaAs crystals for γ-ray Laue lenses: Monte Carlo and experimental results

We report on results of observation of the focusing effect from the planes (220) of Gallium Arsenide (GaAs) crystals. We have compared the experimental results with the Monte Carlo simulations of the focusing capability of GaAs tiles performed with a dedicated ray-tracer. The GaAs tiles were bent using a lapping process developed at the cnr/imem - Parma (Italy) in the framework of the laue project, funded by ASI, dedicated to build a broad band Laue lens prototype for astrophysical applications in the hard X-/soft γ-ray energy range (80-600 keV). We present and discuss the results obtained from their characterization, mainly in terms of focusing capability. Bent crystals will significantly increase the signal to noise ratio of a telescope based on a Laue lens, consequently leading to an unprecedented enhancement of sensitivity with respect to the present non focusing instrumentation

Biological and trophic consequences of genetic introgression between endemic and invasive Barbus fishes.

Genetic introgression with native species is recognized as a detrimental impact resulting from biological invasions involving taxonomically similar invaders. Whilst the underlying genetic mechanisms are increasingly understood, the ecological consequences of introgression are relatively less studied, despite their utility for increasing knowledge on how invasion impacts can manifest. Here, the ecological consequences of genetic introgression from an invasive congener were tested using the endemic barbel populations of central Italy, where the invader was the European barbel Barbus barbus. Four populations of native Barbus species (B. plebejus and B. tyberinus) were studied: two purebred and two completely introgressed with alien B. barbus. Across the four populations, differences in their biological traits (growth, body condition and population demographic structure) and trophic ecology (gut content analysis and stable isotope analysis) were tested. While all populations had similar body condition and were dominated by fish up to 2 years of age, the introgressed fish had substantially greater lengths at the same age, with maximum lengths 410-460 mm in hybrids versus 340-360 mm in native purebred barbel. The population characterized by the highest number of introgressed B. barbus alleles (81 %) had the largest trophic niche and a substantially lower trophic position than the other populations through its exploitation of a wider range of resources (e.g. small fishes and plants). These results attest that the genetic introgression of an invasive congener with native species can result in substantial ecological consequences, including the potential for cascading effects. Supplementary Information: The online version contains supplementary material available at 10.1007/s10530-021-02577-6

Grenzüberschreitungen in Theodor Fontanes Werk. Sprache, Literatur, Medien

Ausgehend vom ‚spatial turn‘ der Kulturwissenschaften fokussiert der Band das seither nur randständig behandelte Thema der Grenze bei Fontane. Untersucht wird die kontinuierliche Präsenz der Grenzüberschreitung in seinem Leben und Werk aus einem literatur- und sprachwissenschaftlichen sowie interkulturellen und intermedialen Blickwinkel, womit die vertiefenden Analysen neue Räume bezüglich der Interpretation von Fontanes Œuvre eröffnen. Der Band enthält 30 Beiträge von Wissenschaftlerinnen und Wissenschaftlern unterschiedlichster Fachdisziplinen aus Italien, Deutschland, Bulgarien, Griechenland, Ungarn und den USA

Einleitung

Ausgehend vom ‚spatial turn‘ der Kulturwissenschaften fokussiert der Band das seither nur randständig behandelte Thema der Grenze bei Fontane. Untersucht wird die kontinuierliche Präsenz der Grenzüberschreitung in seinem Leben und Werk aus einem literatur- und sprachwissenschaftlichen sowie interkulturellen und intermedialen Blickwinkel, womit die vertiefenden Analysen neue Räume bezüglich der Interpretation von Fontanes Œuvre eröffnen. Der Band enthält 30 Beiträge von Wissenschaftlerinnen und Wissenschaftlern unterschiedlichster Fachdisziplinen aus Italien, Deutschland, Bulgarien, Griechenland, Ungarn und den USA